There may be a frequency band in which several kinds of wireless communication systems can coexist. An example of the frequency band is TV whitespace.
TV whitespace refers to unused frequency bands remaining as residual bands owing to the digitalization of analog broadcasting. TV whitespace refers to a spectrum of 512 to 698 MHz allocated to broadcast TV.
When a licensed device is not being used in the corresponding spectrum, an unlicensed device can use the corresponding band.
If it is sought to use TV whitespace, an unlicensed device has to obtain available channels from a corresponding area by utilizing a geo-location database.
Furthermore, in order to solve a coexistence problem between unlicensed devices using TV whitespace, a signaling protocol, such as a common beacon frame, is required.
If IEEE 802.11 is used in TV whitespace, there is an advantage in that coverage is rapidly increased in terms of a spectrum.
However, in most cases, if the coverage is increased, the number of stations is also greatly increased. In this case, there may be a problem in the ability to flexibly handle an increase in the number of users (that is, scalability). Furthermore, since several wireless communication systems and several unlicensed devices coexist, a problem may occur in coexistence. In this environment, scalability may be further degraded according to a Distributed Coordination Function (DCF) and an Enhanced Distributed Channel Access (EDCA) protocol of IEEE 802.11.
The DCF is a channel access mechanism used in IEEE 802.11 and is based on Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). Furthermore, the EDCA corresponds to a contention-based medium access method, from among channel access models which have been proposed by a Hybrid Coordination Function (HCF) defined by extending the existing medium access control protocol of IEEE 802.11. Here, the HCF is a protocol defined in IEEE 802.11e proposed for QoS guarantee.
In order to overcome the above problems and to use the channels of TV whitespace band in an IEEE 802.11 WLAN system, an AP has to have information about channel environments of the TV whitespace band which is continuously changed. Accordingly, there is a need for a sensing method of an AP obtaining and updating information about the channels of TV whitespace band.